This invention relates to scrapers for cleaning the inside walls of tubular members, particularly to scrapers for cleaning the inside of oil well casings and gas well casings.
Modern oil and gas well completions employ the use of casing pipe to protect the integrity of the hole, as a conduit for various tubing and equipment used in exploiting the geographical formations, and to channel the desired oil, gas or other deposits to the surface.
The inside of the casing pipe is subject to the deposit of paraffin wax, grouting cements, rust, and scale. Burrs may occur on the inside of casing walls as a result of downhole operations such as perforation. These foreign materials and burrs act as an impediment in the free passage through the casing of equipment used to complete or work-over the well, and the unimpeded flow of the oil, gas or other deposits from the underground formations.
It has therefore been necessary in the petroleum industry to use scraping devices to scrape the interior of casing walls. To that end, a variety of casing scrapers have been used.
Prior devices used to scrape and clean the inside of well casing employed the rotational effects brought about from using a string of drilling pipe. These devices necessitated the use of rotary drilling equipment. Substantial time and effort is required to assemble the pipe string necessary to carry out a scraping operation with rotary apparatus. Piping scrapers attached to cables allow greater speed and consequently less expense.
Subsequent devices used to scrape and clean the inside of well casing did not require the use of rotational equipment, but depended upon a cutting or scraping action while being pulled up through the well casing. However, these devices suffered form other serious drawbacks. Chief among these drawbacks was the inability to compensate for immoveable restrictions inside the casing pipe while the scraping device was being raised during its pipe scraping mode. The scraper would pass through an obstruction in a downward direction but become lodged when the scraper was pulled upwards to scrape the casing wall. Being unable to compensate for immoveable restrictions, the scraping device would often have to be discarded in the well casing.
The various weights of casing material used in a particular well result in varying internal diameters to be cleaned by the casing scraper. Various attempts have been made to provide casing scraper devices capable of scraping various pipe diameters. Hammer U.S. Pat. No. 2,464,390 and Best U.S. Pat. No. 4,189,000 teach the use of spring means compressed between the mandrel and a plurality of cutting blades, the spring pushing the cutting blade toward the inside casing wall. The arrangement of the plurality of cutting blades and springs necessarily involved results in a complicated structure, each tool having a necessarily limited range of internal casing diameters which can be cleaned. Additionally, should the scraping device extend beyond the lower end of the pipe, the tools cannot be recovered due to the extension of the cutting blades beyond the diameter of the casing.
The prior scraping devices which depend on spring biasing have not historically been capable of withstanding the adverse loads encountered in operation. Due to the necessarily limited size of the spring devices, they are prone to failure.
Harris U.S. Pat. No. 4,706,748 teaches a pipe scraping device attached to a cable which allows the scraper blades to retract when the device is moved downward. However, the scraping device does not allow for retraction of the blades when the device is being raised during its pipe scraping mode. The scraping device may thus pass an immoveable obstruction while moving down the hole and be prevented from passing the obstruction while being pulled up the hole.
It is an object of this invention to provide an effective device for scraping foreign materials from the inside of pipe casing and other tubular materials.
It is a further object of this invention to provide a scraping device for use in oil and gas wells to be used in conjunction with a cable system.
It is a further object of this invention to provide a scraping device for use in oil and gas wells casing capable of compensating for immoveable restrictions inside the casing pipe.
It is a further object of this invention to provide a scraping device for oil and gas wells capable of effectively scraping the inside of pipe casing of varying diameters.
It is a further object of this invention to provide a scraping device for use in oil and gas wells having scraping blades which may be retracted during upward movement of the scraping device to allow movement past immoveable restrictions.
SUMMARY OF THE INVENTION
The foregoing and other objects of this invention are accomplished by providing a casing scraper for scraping foreign materials from the inside of pipe casing and other tubular members. The casing scraper is comprised of a central mandrel supporting a plurality of longitudinally and circumferentially extending scraper blades, the collective configuration of the scraper blades comprising a tube with the mandrel located at the longitudinal axis of the tube structure. Connecting means attach the mandrel to the plurality of scraper blades. Said connecting means are each pivotally attached to the mandrel and to the scraper blades. Adjustable spring means are provided at the base of the mandrel and biased against the underside of the connecting means normally biasing said connecting means at a right angle to the axis of the mandrel, thereby normally positioning the scraper blades at the maximum distance from the mandrel allowed by the length of the connecting means. Upon assertion on the scraper blades of upward pressure or upon assertion on the scraper blades of downward pressure exceeding the spring force, the connecting means may extend at an angle other than ninety degrees from the mandrel, thereby allowing the scraper blades to retract inwardly toward the mandrel. The inward movement of the casing scraper blades is limited by the abutment of the longitudinal edges of the scraper blades. Interlocking extending sections and recesses are provided along the longitudinal edges of the scraper blades to provide continuity of the cutting surface when the blades are in their open position.